1. Technical Field
The disclosure relates to a light source and more particularly to an organic electroluminescent light source.
2. Description of Related Art
Comparing to conventional light sources such as incandescent lamps, fluorescent lamps, and the like, organic electroluminescent light source is light, mercury-free, ultraviolet radiation free, and used as a planar light source. Thus, the organic electroluminescent light source has become a new potential light source. Take a white light organic electroluminescent lamp as an example, a luminescent layer constituted by a blue organic luminescent material and a yellow organic luminescent material is mainly adopted in the conventional technique, where a suitable voltage is applied to the luminescent layer for the organic electroluminescent lamp to emit a white light with specific color temperature.
FIG. 1 is a light spectrum of a conventional organic electroluminescent device. Referring to FIG. 1, although the color temperature of the conventional organic electroluminescent lamp can be controlled by adjusting the voltage applied to the luminescent layer, the color temperature and the light intensity in the conventional organic electroluminescent lamp still have dependency therebetween. In details, when a higher voltage is applied to the luminescent layer, the color temperature of the organic electroluminescent lamp also increases. At the same time, the light intensity of the organic electroluminescent lamp increases along with the increasing color temperature. Similarly, when a lower voltage is applied to the luminescent layer, the color temperature of the organic electroluminescent lamp also decreases. The light intensity of the organic electroluminescent lamp then decreases along with the decreasing color temperature. Consequently, the conventional organic electroluminescent lamp fails to satisfy the manufacturer's needs when the manufacturer demands for light sources with high color temperature and low light intensity or light sources with low color temperature and high light intensity. Further, the color rendering index of the conventional organic electroluminescent lamp can not meet the practical demand (that is, lower than 80). Accordingly, researchers work on developing organic electroluminescent lamps with adaptive color temperature and high color rendering index.